This invention relates to a variable-displacement rotary compressor and, more particularly, to a variable-displacement compressor suitable for an automobile air conditioner.
A conventional variable-displacement rotary compressor is disclosed in a Japanese Utility Model Laid-Open No. 57-58791, where a rotary compressor comprises a housing having a cylindrical inner surface, a thin cylinder rotatably disposed in the inner suface of the housing, and a rotor hoving movable vanes and rotatably disposed in the cylinder with eccentricity with the cylinder so as to define a working chamber defined by a cylinder inner surface and a rotor outer surface, with the working chamber being divided by the vanes into a plurality of sub-chambers. As the rotor rotates, a fluid is sucked from a suction port into a sub-chamber under suction stroke, compressed and then discharged through a discharge port.
The cylinder has an opening for suction of fluid, which opening is substantially the same area and position as an opening formed in the housing so that the fluid is sucked into the sub-chamber through the overlapped opening. The opening extends in a rotating direction of the rotor from a starting point to a termination point. Capacity control of the rotary compressor is effected by shifting the opening of the cylinder relative to the opening of the housing through rotation of the cylinder and changing the overlapped opening area so as to change an amount of suction fluid.
In this compressor, suction of fluid into the working chamber starts when a forward vane of the sub-chamber under suction stroke has passed at the starting point of the suction opening and completes when a backward vane has passed the terminating point of the suction opening. Expressing the suction opening and a vane pitch rotational angles .theta.p, .theta.v of the rotor, the suction is effected by an rotational angle .theta.p+.theta.v. In the capacity control of this rotary compressor, the suction opening rotational angle .theta.p is changed by rotating the cylinder to change the capacity of the compressor. When the capacity is controlled to a minimum capacity, the suction opening rotational angle .theta.p can be changed to zero. However, the vane pitch can not be changed and has a certain value, so that the suction is effected by a rotational angle .theta.v of the vane pitch .theta.v. Therefore, in case of capacity control of the conventional variable-displacement rotary compressor, the minimum capacity is limited.